The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles.
As the information recording density of magnetic recording devices has steadily increased, the size of a magnetic recording mark for a single bit has become very small. Currently, magnetic recording devices are designed primarily with smaller recording bit sizes by reducing the size of a recording magnetic head and reducing the size of magnetic particles of the magnetic recording medium. However, as the magnetic recording density exceeds 1 Tbit/inch2, a concern is that the magnetized information recorded on the magnetic recording medium will disappear in a short time at room temperature due to the effects of thermal vibrations.
One possible way to prevent such undesirable losses is by increasing the coercivity of the magnetic recording medium. However, because there is a limit to the magnitude of a magnetic field generated by the magnetic recording head, it becomes nearly impossible to form the recorded bits on the medium when the coercivity becomes too high.
In order to solve this problem, in the past few years, attention has focused on heat-assisted magnetic recording methods capable of recording on a medium having a high coercivity by heating the medium to lower the coercivity at the instance of recording. One method proposed irradiating a very small light spot at a high power density on the medium to locally heat only the recording region and achieve a high recording density as a heat-assisted magnetic recording method.
Previously, lenses have been used to generate a minute light spot, but recently, the distance between the magnetic head and the magnetic recording medium has become less than 10 nm. Consequently, the problem with optical elements such as lenses being mounted on the magnetic head is, the added weight of the lens causes the magnetic recording head to come into contact with the magnetic recording medium, i.e., the head can no longer reliably float above the medium. In addition, a plurality of magnetic recording media (e.g., disks) are stacked in a magnetic recording device, and the gap between magnetic recording media is usually no more than 1 mm; therefore, the heights of all of the components positioned in the periphery of the magnetic head must be less than the 1 mm gap size. Consequently, mounting optical elements such as lenses on the magnetic head is not desired.
An alternate method for generating a small spot size on the magnetic recording medium without using lenses is a method which forms a light guide path composed of a core and a cladding in a magnetic head. This can be achieved by forming a core having a width and thickness of the order of submicrons in a material having a large refractive index difference Δn with the cladding (explained in further detail below).
Previous light guide paths capable of converting the light spot size, use a light guide path which has a core of several tens of nanometers (nm) and is composed of a highly refractive index material. Moreover, such light guide paths thicken in a tapered shape in the propagation direction of light to couple light having a large spot size compared to the light guide path and reduce the spot size to the order of submicrons as the light propagates in the light guide path.
FIG. 8 depicts a schematic view of the changes in the light intensity profile 26 of the light propagating in a typical example of a tapered core 13 surrounded by a cladding material 23. As shown, the light spot size is reduced as the light following the tapered light guide path core 13 propagates from the narrow upper part of the core width toward the lower part having a wide core width.
Moreover, FIG. 9 depicts the principle of the spot size reduction by the tapered core. The horizontal axis shown in FIG. 9 represents the cross-sectional area of the core, while the vertical axis represents the spot size of the light which can be propagated by the core. According to FIG. 9, a region where the light from the core is propagated while penetrating deeply (i.e., the region indicated by penetration mode in FIG. 9) is used to realize the spot size conversion. According to an example illustrated in FIG. 9, the tapered core tip member P1 finally reaches P2 because the cross-sectional area of the core increases by the thickening of the core in the tapered shape, and the spot size is reduced.
However, in a magnetic recording device adopting such a heat-assisted magnetic recording method, the coupling losses increase and the light utilization efficiency decreases when the light is directly incident on a core having a width and a thickness on the order of submicrons. These undesirable effects are because the spot size of the light emitted from the light source and incident on a light guide path spreads out from several microns (μm), to several tens of microns. To realize heat-assisted magnetic recording, the emitted light power of the light source has been increased which undesirably leads to an increase in the power consumption of the entire magnetic recording device and a temperature increase in the device. In particular, the temperature increase is linked to degradation in the performance of the magnetic recording device.
In order to efficiently couple light having a spot size from several to several tens of microns, the tapered tip size must be less than several tens of nanometers (nm). When the processing precision and fluctuations are considered, the spot size converter is difficult to apply to currently manufactured products. As is clear from FIG. 9, if the refractive index difference Δn between the core and the cladding is small, the tip size can be increased, but the possible eventual reduction in the spot size of light will increase. Thus, a tapered core having a small Δn is not intended for a heat-assisted recording magnetic head with the objective of emitting a small light spot on the magnetic recording medium.
Thus, it is important to form a light guide path having very efficient coupling with light, having a widely spread out spot size, while also being capable of converting this spot to a small light spot without light losses in the magnetic head. Moreover, it may be preferable to provide a mechanism which can irradiate light having a reduced spot size on the order of submicrons with high light utilization efficiency on a magnetic recording medium by using a spot size converter formed in the magnetic recording head in a magnetic recording device having a small, lightweight optical element mounted on the magnetic head.